In this kind of fuel cell, although an electrolyte membrane is constituted by using a polymer ion-exchange component, it is required that it should have good high-temperature strength since it is used under temperature around 100° C.
Conventionally, such means is adopted that ion-exchange capacity is sacrificed by giving priority to the high-temperature strength of an electrolyte membrane.
However, according to the conventional means, there is a problem that a power-generating performance level cannot but become low because ion-exchange capacity is low.
In a solid polymer fuel cell, a proton moves with entrained water toward an oxygen electrode from a fuel electrode in an electrolyte membrane. Therefore, since the fuel electrode easily becomes dry, there is a possibility that proton conductivity may decrease. On the other hand, when water produced by an electrode reaction becomes excessive on the oxygen electrode, a flooding phenomenon (a phenomenon in which a diffusion path of a gas is blocked by an oxygen electrode getting wet) arises. For this reason, it is necessary to remove moisture on the oxygen electrode while supplying moisture on the fuel electrode.
For such moisture control, (a) a method of humidifying an electrolyte membrane through fiber by making the electrolyte membrane have sandwich structure by sandwiching twisted yarn-formed fiber, and (b) a method (refer to Japanese Patent Application Laid-Open No. 10-334922) of adding a water adsorbent to the fuel electrode etc. are proposed. However, the method (a) has a problem that ion conductivity decreases since the thickness of the electrolyte membrane increases by the fiber, and the method (b) has a problem that the ion-exchange capacity of the fuel electrode and the like decreases by the addition of the water adsorbent.